The present invention relates to a photo detector for a data input device for example an optical mouse, and more particularly to such a photo detector which effectively eliminates interference of proximity light from photo sensor chips, so as to improve signal receiving accuracy.
A photo encoder used in a mouse, as shown in FIG. 1, is generally comprised of at least one encoding grid wheel 60 turned with a revolving shaft 50, the wheel 60 having light permeable portions 61 and light tight portions 62 alternatively arranged around the periphery, a light source 70, and a photo receiver element 80. The photo receiver element 80 comprises a set of photo sensor chips 81 adapted to receive light from the light source 70 through the light permeable portions 61 of the wheel 60. When the wheel 60 is turned with the revolving shaft 50, the light permeable portions 61 and the light tight portions 62 are moved to cut through light from the light source 70, causing working light beams to be produced. When the photo chips 81 receive a working light beam an energy is produced. When the wheel 60 is continuously turned, sine waves are obtained through a wave form monitor, and four signals (0,0);(0;1);(1;1);(1;0) are obtained through a rectifier circuit (see FIG. 2). However, because the light receiving side of the photo receiver element 80 and the light emitting side of the light source are of a planar design, a diffused light will be produced, thereby causing an interface. Referring to FIGS. 3 and 4, when the wheel 60 is turned, the photo sensor chips 81 are induced by working light beams from the light source 70 to produce sine waves A;B, causing a rectifier circuit to produce square waves A1;B1. When working light beams 71 enter the photo receiver element 80, diffused light C is produced, causing an interference to the photo sensor chips 81. Referring to FIG. 4A, the waveform B is theoretically a sine wave, however the photo sensor chips 81 are energized by diffused light to produce a sine wave X before arrival of working light beams 71. Because of the effect of diffused light C, the photo sensor chips 81 are induced to produce an energy before arrival of working light beams 71, and diffused light C causes the photo sensor chips 81 unable to release energy after leaving of working light beams 71. Because of the aforesaid problem, the wave form monitor cannot accurate obtain sine wave energy values from the sine waves A;B. and the rectifier circuit cannot produce square waves exactly same as the square waves A1;B1.